1. Field of the Invention
The present invention relates generally to mobile construction machines and particularly, but not by way of limitation, to a self-propelled milling machine for removing pavement material.
2. Description of Related Art
Typically, construction machines are either track-mounted or wheel-mounted for movement over a surface. A track-mounted milling machine is disclosed in U.S. Pat. No. 4,325,580. Track assemblies are capable of supporting a great deal of weight and provide good stability for construction machines.
There are several disadvantages associated with tracks, however. Tracks are relatively expensive to manufacture and to maintain. In addition, it is not permissible to drive track-mounted heavy equipment on paved surfaces in some regions. Moreover, tracks generally limit the speed of a construction machine to about three mph and the turning radius to around 30 degrees.
Construction machines may also be equipped with pneumatic tires. Obviously, the likelihood of punctures is one problem with placing pneumatic tires on a construction machine. In addition, a high-pressure pneumatic tire has an upper weight-carrying limit of about 12,000 pounds and generally restricts the speed of a machine to 5 mph or less. An even greater problem with pneumatic tires, however, is their bounce. Bounce has a severely adverse effect on the stability of the machine and stability is extremely important in the operation of a machine such as a milling machine.
Hard rubber tires may be utilized in place of pneumatic tires on construction machines. Of course, hard rubber tires are not susceptible to punctures. For this reason, hard rubber tires have been used on fork-lifts and loaders in scrap yards and steel mills. In addition, hard rubber tires have good load-bearing characteristics.
Hard rubber tires perform acceptably on sufficiently strong paved surfaces, but tend to break through many pavements. In off-pavement applications, hard rubber tires do not have good traction because they do not deform to increase the surface area of the tire in contact with the ground.